Hi Mike,

On Sun, Mar 03, 2013 at 02:54:24AM -0800, Mike Turquette wrote:

Quoting Richard Zhao (2013-03-02 00:22:19)

quoted

On Fri, Mar 01, 2013 at 06:55:54PM -0800, Bill Huang wrote:

quoted

On Sat, 2013-03-02 at 04:48 +0800, Mike Turquette wrote:

quoted

Quoting Mike Turquette (2013-03-01 10:22:34)

quoted

Quoting Bill Huang (2013-03-01 01:41:31)

quoted

On Thu, 2013-02-28 at 12:49 +0800, Mike Turquette wrote:

quoted

Dynamic voltage and frequency scaling (dvfs) is a common power saving
technique in many of today's modern processors.  This patch introduces a
common clk rate-change notifier handler which scales voltage
appropriately whenever clk_set_rate is called on an affected clock.

I really think clk_enable and clk_disable should also be triggering
notifier call and DVFS should act accordingly since there are cases
drivers won't set clock rate but instead disable its clock directly, do
you agree?

quoted

Hi Bill,

I'll think about this.  Perhaps a better solution would be to adapt
these drivers to runtime PM.  Then a call to runtime_pm_put() would
result in a call to clk_disable(...) and regulator_set_voltage(...).

There is no performance-based equivalent to runtime PM, which is one
reason why clk_set_rate is a likely entry point into dvfs.  But for
operations that have nice api's like runtime PM it would be better to
use those interfaces and not overload the clk.h api unnecessarily.

Bill,

I wasn't thinking at all when I wrote this.  Trying to rush to the
airport I guess...

clk_enable() and clk_disable() must not sleep and all operations are
done under a spinlock.  So this rules out most use of notifiers.  It is
expected for some drivers to very aggressively enable/disable clocks in
interrupt handlers so scaling voltage as a function of clk_{en|dis}able
calls is also likely out of the question.

Yeah for those existing drivers to call enable/disable clocks in
interrupt have ruled out this, I didn't think through when I was asking.

quoted

Some platforms have chosen to implement voltage scaling in their
.prepare callbacks.  I personally do not like this and still prefer
drivers be adapted to runtime pm and let those callbacks handle voltage
scaling along with clock handling.

Voltage scaling in clock notifiers seems similar. Clock and regulater
embedded code into each other will cause things complicated.

Hi Richard,

Sorry, I do not follow the above statement.  Can you clarify what you
mean?

As we have agreement that a operating point may have multiple clocks
and regulators, this patch is impossible to support multi clocks. And
it might mislead dvfs implementer to use clock notifier. It may be good
to have unified api like dvfs_set_opp(opp), or drivers can handle clocks
and regulators theirselves which is more flexible. What do you think?

Thanks
Richard